Paper making with synthetic fibers



June 18, 1963 c. B. MOORE 3,094,454

PAPER MAKING WITH SYNTHETIC FIBERS Filed Jan. 5. 1961 United StatesPatent 3,094,454 PAPER MAKING WITH SYNTHETIC FIBERS Charles B. Moore,Scituate, Mass., assignor to W. R.

Grace & (10., Cambridge, Mass, a corporation of Connecticut Filed Jan.3, 1961, Ser. No. 80,431 4 Claims. (Cl. 162-157) This invention isconcerned with the manufacture of paper and similar materials fromthermoplastic fibers which are not amenable to being handled inconventional paper-making equipment.

Cellulose fibers coated with a polyolefin have recently becomeavailable. For example, see Belgian Patent No. 575,559, dated February10, 1959, issued in the name of National Lead Company. These fibers arehydrophobic and display no, or very little, fiber-to-fiber bonding orcohesiveness when formed as a Wet web in a conventional paper-makingmanner. There is, however, a desideratum for forming paper in largevolumes from these fibers because of their unusual properties, e.g.chemical inertness, pore structure, and thermoplasticity.

In brief compass, the present invention is a paper-making processcomprising forming an aqueous slurry or papermaking stock of asurfactant and hydrophobic polyolefin coated cellulose fibers in thehead box of a paper-making machine. The paper-making machine isconventional and has a moving endless filter screen. The filter screensupports a smooth surface fabric felt having a relatively low draintime. The stock is flowed on to the felt and the water is drainedtherefrom through the felt and screen, forming a web of the fibers onthe felt. The web so formed is then dried of water, while stillsupported by the felt. Mechanical compaction of the web and felt isavoided as much as possible. The dried web is immediately thereafterheated to a softening temperature in the range of 250 F. to 350 F. tofuse the polyolefin and impart coherency to the web. The web isthereafter cooled and stripped from the felt to obtain a self-supportingweb of the polyolefin coated fibers that could not be obtained in anyother manner at comparable production rates.

This invention will become clear from the following discussion anddescription of the drawing attached to and forming a part of thisspecification. The drawing illustrates the application of the principlesof this inventlon to the formation of a coherent web of thermoplasticfibers using one type of cylinder paper-making machine.

The fibers used in the present invention are basically cellulose fiberscoated with a polyolefin such as a polystyrene, polybutadiene orpolyisoprene, but preferably a polyethylene, a polypropylene, ormixtures thereof. The cellulose fibers give shape to the polyolefin. Thecellulose typically has an average length of about 1 to 20 milli metersalthough any length that can be formed into a paper can be used. Thecellulose fibers can be any of those conventionally used forpaper-making such as bleached or unbleached hard or soft wood sulphitesor sulphates, soda-flock, cotton linters, manila hemp and syntheticfibers. The polyolefin can be placed on the fibers through the use ofsolvents, but it is preferred to form the polyolefin in situ by firstimpregnating the cellulose, while carried in finely divided form in ananhydrous hydrocarbon liquid with a polymerization catalyst, such as atitanium or zirconium compound, followed by contact with the monoolefinunder polymerization conditions. The polyolefin comprises to 75 weightpercent of the reaction product and the remainder is cellulose. Thepolyolefin preferably has a softening point in the range of 250 F. to350 F. The polyolefin essentially coats all of the fibers and some of itwill usually appear as nodules on the fibers.

A paper-making slurry is formed from the thermoplastic ice fibers by theuse of a surfactant, since the fibers are hydrophobic. Such surfactantsas polyethylene glycol terdodecyl thioether (Nonic 218),polyoxyethylated fatty alcohols (Emulphor ON-870) and the dioctyl esterof sodium sulfosuccinic acid (Aerosol OT) are satisfactory. The amountof surfactant used will vary, but will usually be in the range of 0.05to 0.1 Weight percent based on dry fibers. The consistency of the stockis about 0.01 to 1 percent, preferably 0.01 to 0.1 percent (dry basis).The fibers do not respond to mechanical action such as heating in aconventional manner. They can be dispersed in water by simple agitation,with any lumps being mechanically dispersed as is necessary. The fibersare very loose, usually giving freeness readings above 700 cubiccentimeters Canadian Standard. No additional binders, such as glue andstarch, are necessary or desirable.

The sheet or felt used to support the web until it is rendered coherentin accordance with this invention can be a woven material such as acheese cloth, or it can be a nonwoven material. It has a relativelysmooth surface to prevent undue adhesion of the fibers to the web. Thefelt is relatively open and does not materially alter the water drainagerate and the rate of paper formation from that obtained with the screenalone. The felt should allow 400 cubic centimeters of air to passthrough 8 plies in 4 to 10 seconds as measured with a Gurley densimeterequipped with a 5 ounce cylinder and A inch diameter orifice. Slowerdraining felts have been used, however, by slowing the machine downsufficiently to compensate for the slow drainage. It is preferred to usefelts made from nonwovens because they are inexpensive and can bediscarded after several passes through the machine. While a continuousself-returning belt of Woven fabric might possibly be used, it ismechanically difiicult to provide for the extreme lengths necessary tosupport the web from the head box to the final heating and fusion step.

Either a Fourdrinier or a cylinder machine can be used. The supportingfelt is placed onto the Wire screen of the paper-making machine prior tothe laying down of the stock. The stock is flowed onto the web in anamount sufiicient to obtain the desired thickness, usually 10 to 400pounds of fiber per 3000 square feet, and is drained and at leastpartially dried before the fusion step.

It is the custom in most paper-making processes to mechanically pressthe Web to squeeze Water therefrom before resorting to heat drying. Thisresults in some compaction of the Web, and in the present process, someintermingling of the web fibers with the felt, making the finalstripping or separating of the felt and web more difficult. It ispreferred, therefore, not to subject the webfelt strip to severemechanical compaction or compression by rolling or similar methods priorto the fusion step.

The web is set or fused as by running it over a heated roller or canthrough an infrared unit or through an air or festoon dryer, and heatingit to a temperature sufiicient to permit contiguous fiber bonding. Totalfusion of the fibers need not be carried out at this point. It issatisfactory if sufficient bonding takes place to give the web enoughcoherency to be self-supporting under whatever additional treatment maybe desired. After the web fusion step, the webis allowed to cool and isthen separated from the felt by simple stripping.

The papers thus obtained can be fabricated into excellent batteryseparators by pressing between heated plates having the desiredconfiguration. Depending on the polyolefin content, the paper will alsofind use per se as a filter medium, especially for corrosive materials,as a coating base, and as a cushioning or packing material. The papersof relatively high polyolefin content can readily be molded intodisposable cups and dishes, milk bottles, and floor tiles.

Example A polyethylene coated cellulose is prepared as follows.

Reactants: Weight percent Solka-Floc 47.0 Toluene 23.7 TiCl 11.8 CH MgBr17.5

Disperse the Solka-Floc (a pure alpha cellulose) in the toluene(anhydrous), and react the titanium tetrachloride therewith for one hourat room temperature under a nitrogen atmosphere. Add the methylmagnesium bromide and raise the temperature to 131 F. Bubble ethylenetherethrough at a pressure of 25 pounds per square inchuntil an-amountby weight about equal to the cellulose has been added. Cool the solutionand add an equal volume of methanol. Follow by filtering and washingwith additional methanol. A white powdery fiber containing about 50weight percent polyethylene is obtained after desiccation. Thepreparation of the thermoplastic fibers is known to the prior art and isnot part of the present invention.

A stock'having the consistency of two percent is made from the fibersusing 0.1 weight percent on dry fibers of sodium dioctylsulfosuccinateas a dispersant, by simple admixing in a pulper. The stockhas a freeness of about 760 cubic centimeters Canadian Standard. Thestock is then diluted to a consistency of 0.05 percent.

With-reference to the drawing, the diluted stock is added to the headbox 1 of a cylinder machine 2, eg a Rotoformer (trademarkofSandy HillIron and Brass Works). The cylinder carries a screen having a diameterof about 48 inches. The cylinder is equipped with suction boxes 3. Thecylinder forms a paper strip 29 inches wide at a rate of 20' feet perminute. The dry weight of the paper web is 220 pounds per 3000 squarefeet (500 sheets, 24 inches by 3 6 inches) The felt is picked up by thecylinder from feed roll 4 prior to the head box. The felt passes betweenthe head box apron and the cylinder wire, the web is deposited thereonand the continuous web-felt sheet then passes under a light couch roll5. The felt is a nonwoven, formed from air laid cotton and nylon fibersover /2 inch long, and bonded together with a small amount ofbutadiene-styrene elastomer. It has a ream weight of 36 pounds (500-sheets 24 inches by 36 inches), at caliper of 0.011 inch, and an S-plyGurley densimeter t me of 4.2

seconds (5 ounce cylinder, 400 cubic centimeters, 4 inch opening). Thisnonwoven is commercially available as Lantuck 4400T Prebond sold by WestPoint Manufacturing Company.

The strip is passed from cylinder 2 to a series of twenty dryingdrums'7, only a part of which isshown and heated to about 300 F. Thedrums are four feet in diameter. The moisture content of the web isreduced by the drying to about three percent. The web is then passed tofusion rolls 8 where the web is heated momentarily to a temperature of325 F. It is then allowed to cool while passing over roller 10 which iswater cooled. A high velocity jet dryer has also been used to dry andset the web.

The web-felt strip is then passed through stripper rolls 11 with thefelt being Wound up on roll 13 for reuse. The total linear distance oftravel from the head box to the stripping rolls is about 130 feet. Thetwenty feet per minute rate of this example is low compared tocommercial practice. At commercial speeds it would be impractical toprovide for continuous return of the felt. Conventional splicingarrangements are provided at feed roll 4 to provide continuous additionof the felt to the process.

The web stripped from the felt is shown as being wound on wind-up roll14. It ma, however, be directly passed on to whatever furtherconventional treatment may be desired, such as calendering,impregnation, or coating. The web obtained as described is buff coloredand has a caliper of mils.

While the preparation of a fairly heavy paper has been described, itwill be appreciated that the process of this invention also permitsrelatively thin papers to be formed from the polyolefin coated fiberswithout difficulty because of the support given by the felt.

\ Conventional pulps, especially of long fibers (10 to 20 millimetersaverage length) can be added to the stock in amounts up to 20 weightpercent of the coated cellulose, which is insufficient to giveself-supporting characteristics to the wet web.

Having described this invention, what is sought to be protected byLetters Patent is succinctly set forth in the following claims.

What is claimed is:

1. A paper-making process comprising flowing an aqueous paper-makingstock of a surfactant and hydrophobic polyolefin coated cellulose fibersfrom the head box of a paper-making machine having a moving, endlessfilter screen onto a relatively smooth surfaced felt supported by saidscreen, drawing the water thereof through said felt and screen formingthereby a Web of said fibers on said felt, drying and fusing thepolyolefin content of said fibers by heating said web while supported bysaid felt and prior to any appreciable mechanical compaction thereof toa temperature in the range of 250 F. to 350 F., cooling the web, andstripping said web now in coherent form from said felt.

2. The process of claim 1 wherein said polyolefin is polyethylene formedin situ on said cellulose by the catalytic polymerization of ethylene oncatalyst impregnated cellulose fibers carried in an anhydrous liquidhydrocarbon, said polyethylene amounting to about 10 to weight percentof the fibers.

3. The process of claim 2 wherein said felt is an air laid nonwovenmaterial comprised of cotton and nylon fibers bonded together with aminor amount of an elastomer.

References Cited in the file of this patent UNITED STATES PATENTS MilkeyApr. 19, 1932 Hanson Sept. 13, 1949

1. A PAPER-MAKING PROCESS COMPRISING FLOWING AN AQUEOUS PAPER-,AKINGSTOCK OF A SURFACTANT AND HYDROPHOBIC POLYOLEFIN COATED CELLULOSE FIBERSFROM THE HEAD BOX OF A PAPER-MAKING MACHINE HAVING A MOVING, ENDLESFILTER SCREEN ONTO A RELATIVELY SMOOTH SURFACED FELT SUPPORTED BY SAIDSCREEN, DRAWING THE WATER THERETO THROUGH SAID FELT AND SCREEN FORMINGTHEREBY A WEB OF SAID FIBERS ON SAID FELT, DRYING AND FUSING THEPOLYOLEFIN CONTACT OF SAID